Numerous processes are known for the preparation of toners, such as, for example, conventional processes wherein a resin is melt kneaded or extruded with a pigment, micronized, and pulverized to provide toner particles. Emulsion aggregation (EA) toners are used in forming print and/or xerographic images. Emulsion aggregation techniques typically involve the formation of an emulsion latex of resin particles that have a small size of from, for example, about 5 to about 500 nanometers in diameter, by heating the resin, optionally with solvent if needed, in water, or by making a latex in water using an emulsion polymerization. A colorant dispersion, for example of a pigment dispersed in water, optionally with additional resin, is separately formed. The colorant dispersion is added to the emulsion latex mixture, and an aggregating agent or complexing agent is then added and/or aggregation is otherwise initiated to form aggregated toner particles. The aggregated toner particles are heated to enable coalescence/fusing, thereby achieving aggregated, fused toner particles.
Toner systems normally fall into two classes: two component development (TCD) systems, in which the developer material includes magnetic carrier granules having toner particles adhering triboelectrically thereto; and single component development (SCD) systems, which generally use only toner. Of the SCD systems, both magnetic and non-magnetic systems are known. Magnetic systems involve the use of a toner containing a magnetic substance, which may preclude the development of sharp color images, which has led to a focus on non-magnetic systems.
The operating latitude of a powder electrophotographic development system may be determined to a great degree by the ease with which toner particles may be supplied to an electrostatic image. Placing charge on the particles, to enable movement and development of images via electric fields, is often accomplished with triboelectricity. Triboelectric charging may occur either by mixing the toner with larger carrier beads in a TCD system, or by rubbing the toner between a blade and donor roll in an SCD system.
With non-magnetic SCD systems, toner is supplied from a toner house to the supply roll and then to the development roll. The toner is charged while it passes a charging/metering blade. Non-magnetic SCD has been very popular for desk top color laser printers due to its compact size, since it does not need a carrier in the development housing to charge toner. Non-magnetic SCD systems may thus utilize cartridges that are smaller in size compared with TCD systems, and the cost to a customer to replace a unit may, in some cases, be lower for a single component development system compared with a two component system.
There are several issues associated with SCD systems. The first is low charge and broad charge distribution on toner particles compared with conventional TCD toner. This is because the time for toner to flow through the gap between the blade and the development roll is very short. Low charge causes high background and low developability. Toner for SCD systems also has a high fines content, which may affect the charge and the print background. Also, the higher the fines content, the broader the charge distribution.
Another issue with SCD systems includes toner robustness in aging and in extreme environments such as A and C zone conditions found in an electro photographic apparatus. The high stress under the blade may cause the toner to stick to the blade or the development roll. This may reduce the toner charge and the toner flowability. Since non-magnetic toner is charged through a charging/metering blade, low charging and low flowability can cause print defects such as ghosting, white bands, and low toner density on images.
There remains a need for a toner composition suitable for high speed printing, particularly high speed monochrome printing that can provide excellent flow, charging, lower toner usage, and reduced drum contamination.